The end customer (shop owners/your customers) are responsible for any fees incurred if/when transported across international boarders.
Shipments outside of the United States may encounter custom duty fees. The fees are based on the destination and the regulations the country being shipped to. Different countries have import procedures which is determined by its custom’s law in the destination country, not Kin Custom or the carrier.
Typically, the type of goods shipped and the value of that good are factors determining custom duties and taxes. Ultimately, the end customer will be responsible for paying the customs duty. As a shop owner, when setting your retail price it's important to keep in mind many custom fees are charged based on the retail price of the good. It's recommended to share this may be an unexpected cost to your customers and to include on your checkout page before the transaction is made.